1. Field of the Invention
This invention relates to an electromagnetic proportional flow control valve for controlling the valve opening degree in proportion to the electromagnetic force (excitation current), and in particular to a valve of such type to be used for the fuel-air ratio control or the idle-rotation control of the engine of a vehicle.
2. Description of Prior Art
A conventional proportional flow control valve is disclosed in, for example, Japanese Utility Model Registration Publication No. 57-143459 which was published without examination on Sept. 8, 1982. In the conventional valve, for assuring the operation thereof with reliability, a pressure chamber is formed so as to cancel the opposite pressures applied to the valve member. For establishing the pressure chamber, a bellows is used and is disposed between the valve member and the housing. The valve member is supported on a lengthwise shaft which is moved by an electromagnetic solenoid in the axial direction.
However, for carrying the shaft, at least a pair of bearings have to be provided and the solenoid must have a sufficient power in light of the weight of the shaft itself and the friction between the shaft and each bearing. Further, for enduring repeated expansion and shrinkage, the bellows has to be made from polytetrafluoroethylene, which is very expensive.